In the oilfield industry, well applications often employ a variety of sensors coupled to downhole equipment to provide information relative to the well or equipment during a given application. For example, temperature, pressure, and other well conditions may be monitored as well as readings related to the equipment itself. These equipment readings may involve the monitoring of load and/or pressure imparted on the equipment during an application.
Downhole equipment may include downhole tractors, for example, to drive a downhole tool through a horizontal or highly deviated well at an oilfield. In this manner, the tool may be positioned at a well location of interest in spite of the non-vertical nature of such wells. Different configurations of downhole tractors may be employed for use in such a well. For example, a reciprocating or “passive” tractor may be utilized which employs separate adjacent sondes with actuatable anchors for interchangeably engaging the well wall. That is, the sondes may be alternatingly immobilized with the anchors against a borehole casing at the well wall and advanced in an inchworm-like fashion through the well. Alternatively, an “active” or continuous movement tractor employing tractor arms with driven traction elements thereon may be employed. Such driven traction elements may include wheels, cams, pads, tracks, or chains. With this type of tractor, the driven traction elements may be in continuous movement at the borehole casing interface, thus driving the tractor through the well.
Regardless of the tractor configuration chosen, the tractor, along with several thousand pounds of equipment, may be pulled thousands of feet into the well for performance of an operation at a downhole well location of interest. It is over the course of such applications that monitoring conditions of the well and/or equipment with a sensor as noted above may be of particular benefit. For example, as the equipment is positioned deeper and deeper within the well, the load of the tractor assembly may approach a level that is beyond the load capacity of the tractor. Thus, monitoring load may play a significant role in carrying out such an operation. Therefore, a load sensor may be incorporated into the tractor assembly.
Whether it be load, pressure or another condition being monitored, it is likely that the sensor is of a conventional strain gauge configuration. Generally, this includes the use of four leads that are run between the sensor and a microprocessor. These leads include two exitation leads, one for power, the other for ground. Two output leads are also provided to transmit data between the sensor and the microprocessor.
Space available on the downhole tractor comes at a premium. That is, the well may offer less than about 12 inches in diameter to work with. Thus, the profile of the tractor may be minimal. As a result, features incorporated into the body of the tractor may be of limited sizing as well. The same may go for the overall amount of features employed in conjunction with the tractor. Indeed, the amount of wiring that is employed downhole may even be kept at a minimum. For example, where a downhole sensor is employed as described above, the downhole microprocessor may be positioned relatively near the sensor. In this manner, the amount of wiring may be kept at a minimum. This may be particularly beneficial in the case of a downhole sensor which is likely to make use of numerous wiring leads, generally about four, as also noted above.
Unfortunately, even where a relatively short distance is utilized between the microprocessor and the sensor, a substantial amount of wiring may still be present over such a distance. For example, a separation of no more than about four inches between the sensor and the microprocessor still results in at least 16 inches of wiring due to the numerous leads employed by the sensor. As a result, many tractor assemblies fail to employ downhole sensors in order to preserve space. This may be particularly true for assemblies that would require retrofitting in order to accommodate such a sensor.